J-shell developer housing

ABSTRACT

Shell developer for electrostatic imaging apparatus. The shell structure is characterized by a J-shaped configuration having disposed within the shell a partition and baffle arrangement which effects movement of carrier particles and unused toner such that they are mixed with newly dispensed toner as the former and the latter strike the baffle which is disposed above the developer supply level in the shell.

United States Patent Roth, Jr. et al.

[54] J -SHELL DEVELOPER HOUSING [72] lnventors: Charles F. Roth, Jr., Rochester; Gordon C. Butler, Fairport, both of 1 Aug. 8, 1972 6/1969 Chawdaetal ..ll8/637 .3/1970 Gundlach ..ll7/17.5

Primary Examiner-Morris Kaplan Assistant Examiner-Leo Millstein Attorney-James J. Ralabate, John E. Beck and Benjamin B. Sklar [57] ABSTRACT Shell developer for electrostatic imaging apparatus. The shell structure is characterized by a .l-shaped configuration having disposed within the shell a partition and baffle arrangement which effects movement of carrier particles and unused toner such that they are mixed with newly dispensed toner as the former and the latter strike the battle which is disposed above the developer supply level in the shell.

5 Claim, 2 Drawing Figures PATENTEDAUB 8 I972 3,682,137

PRIOR ART INVENTOR. CHARLES E ROTH.JR B GORDON C. BUTLER BACKGROUND OF THE INVENTION This invention relates, in general, to electrostatic imaging and, more particularly, to structure for developing electrostatic images.

In one form of electrostatic recording, as disclosed by Carlson in US. Pat. No. 2,297,691, a plate comprising a conductive backing upon which is placed a photoconductive insulating material, is unifomily charged and subsequently exposed through a suitable lens and lamp combination to an object to be reproduced. The photoconductive material or coating becomes conductive in accordance with light patterns through the lens thereby discharging certain areas of the unifonn charge leaving a latent electrostatic image thereon. The development of the latent image is generally effected by electrostatic attraction of finely divided pigmented resin to the latent image, the amount of charge found in image areas determining the amount of resin attracted thereto. The amount of charge remaining on the plate after exposure is proportional to the image density of the original, consequently, areas of lesser charge concentration result in deposits of lower toner or resin density while the areas of greater charge concentration become proportionally more dense. A permanent record of the object is obtained through transfer of the developed latent image to a permanent record media with subsequent fixing of the resin.

Various pigmented resins have been employed for the purpose of developing a latent electrostatic image. The toner material, as these resins are commonly referred to, is generally conveyed to the image areas by means of a relatively larger and coarser material known as a carrier, the carrier being adapted to support a quantity of toner upon its surface. Thus the developer constitutes a two-component mixture which components are selected such that the materials interact electrostatically when brought into rubbing contact thereby causing a triboelectric attraction therebetween.

While many workable development systems are known to those in the art of electrostatic recording, most of them have been found to be impractical, commercially, because they are too complex and therefore incompatible with automatic machines or because they are inefficient or too costly. Cascade development of electrostatic images as disclosed in US. Pats. Carlson, Walkup et al. No. 2,573,881 and to Calson, No. 2,990,278, because of many advantages, has become the most commonly used method of development.

The cascade development process in automatic systems comprises a developing unit including an outer container or cover with a trough at its bottom containing a supply of developing material. The developing material is picked up from the bottom of the container and dumped or cascaded over the surface of the xerographic plate by a number of buckets on an endless driven conveyor belt. This development technique utilizes a two-element development mixture including finely-divided, colored, marking particles or toner and grossly larger carrier beads. The carrier beads serve both to deagglomerate the toner particles and to charge them by virtue of the relative position of the toner and the carrier material in the triboelectric series. Thus,

friction between the beads and toner particles during tumbling of the developing mixture causes them to charge to opposite polarities so that the toner particles cling to the carrier beads. When the carrier beads with 5 toner particles clinging to them are cascaded over the xerographic plate, the electrostatic fields from the latent electrostatic charge pattern on the plate pull toner particles off the carrier beads serving to develop the image. The carrier beads, along with any toner particles not used to develop the image, then fall back into the bottom or trough of container for reuse, with the toner being periodically replenished. Although this type of system works quite well, it does require a rela- 15 tively large amount of space, bulky conveyors and other components thereby increasing greatly the overall size and cost of the reproducing apparatus.

Disadvantages of development systems, especially, those associated with cascade development, have recently (i.e. to other methods of development, for example, one where the generally upward movement of an imaging surface contacts the developer supply contained in an arcuate housing or casing structure. Upward or uphill flow of developer material is accomplished at the interface between the developer and the imaging surface due to inherent frictional forces. These frictional forces are sufficient to carry the developer material along in tumbling contact with the moving surface at a slightly lower speed and it tumbles so that new toner particles are always being presented to the plate surface by the rotating carrier. Although not clearly understood, it is believed that the development is effected during the period of flowing contact by means of the classical development scavenging concept as disclosed in the aforementioned Walkup and Carlson patents. The developer material i.e., unattracted toner and carrier beads) upon being released from the imaging surface, returns to the developer supply via the far side of the developer housing and approximately the top of the developer supply where it is replenished with toner before circulating back to the zone of active development. Although this flow-contact system satisfactorily overcomes some of the previously mentioned disadvantages, it has certain inherent disadvantages. For example, newly added toner stagnates in voids in pockets of the housing and thus, never enters the zone of active development.

Accordingly, the general object of this invention is to provide a new and improved electrographic or electrophotographic recording apparatus.

Another object of this invention is to provide structure for mixing newly dispensed toner and already used developer material prior to their return to the developer supply.

BRIEF SUMMARY OF THE INVENTION Briefly, the above-cited objects are accomplished by the provision of a shell developer structure or housing having a generally J-shaped configuration in cross secdeveloper by frictional forces created, upwardly between the web and the partition. The distance between the two is substantially constant such that developer is carried to the top edge of the partition where it moves over to the opposite side thereof. A toner dispenser is positioned over the shell intermediate the partition and the outer wall of the shell thereby allowing newly added toner to be mixed with already used developer prior to their return to the developer supply. To enhance the mixing or cross action process, a baffle structure is interposed between the toner dispenser and the developer supply such that the newly added toner and the already used developer simultaneously strike the baffle.

BRIEF DESCRlPTlON E THE DRA'WTNGS E or a better understanding of the invention as well as further objects and features thereof, reference may be had to the detailed description of the invention to be read in connection with the accompany drawings wherein:

FlG. l is an illustration of the basic flow-contact concept of developer mixing as found in the prior art; and

PM]. 2 is an elevational view of recording apparatus representing the invention.

DETAILED DESCRllPTlQN OF THE PREFERRED EMBODTMENT Referring now to the drawings, especially ElG. ll, reference character ll ll designates generally a structure which diagrammatically depicts the basic flow-contact system which as noted hereinabove is found in the prior art. A drum 1111 is rotated so as to move in the direction indicated through a cresent-shaped housing 32. The housing contains sufficient developer material so that the drum surface continually moves in contact with the developer material as it moves through the housing. The developer material 113 constitutes a twoelement mixture including finely-divided, colored marking particles or toner and grossly larger carrier beads. A frictional force is established between the moving drum surface and the developer material causing a thin layer of developer material adjacent to the drum surface to move in an uphill direction. The upward movement of developer material creates a void at the bottom of the housing which is filled as the entire back layer of developer moves down more or less as a unit. A flow of developer material is thus established within the housing as indicated by the arrows. Satisfactory results have been obtained using semi-micro toner particles on the order of 5 microns in combination with uncoated nickel carrier beads on the order of 450 microns in size.

The path followed by the uphill flow of developer material as it moves in contact with the drum surface describes the active development zone. Theoretically, properly charged and toned developer material is delivered to the start of the active development zone from the supply of developer material found on the back side of the system. The developer material develops a latent image on the drum as it flows along in contact with the drum through the active development zone. At this time, toner is electrostatically attracted from the carrier material to the more highly charged image areas. Because of the relatively gentle action of All the flow established within the housing, little or no toner is mechanically dislodged from the carrier material. The developer material continues to move along in contact with the moving drum surface until the frictional forces holding it to the drum are overcome, as for example by the drum moving out of contact with the developer material. The relatively depleted developer material returns to the back side of the system where it is replaced as it moves down to fill the void left by the continuous flow of upwardly moving material. It can be seen that the uppermost edge of the housing 12 is spaced farther from the drum llll than other portions thereof. This spacing coupled with the aforementioned movement of the drum away from the developer allows the forces of gravity to effect return of the developer material as previously mentioned.

While a system, as shown in lFlG. l, is simple in construction, durable and inexpensive to make, its performance is not totally satisfactory because toner stagnates in pockets which prevents proper mixing and it is a relatively slow process due to the relatively brief contacting of recording surface and developer. An improvernent in the latter respect is described in US. Pat. No. 3,448,724 issued in the name of Chawda et al., wherein the contact period of developer and recording medium is longer thereby allowing for faster operation. The hawda et al. construction also exhibits improved developer mixing, however it does not represent the optimum.

The improved recording apparatus constituting the invention is shown in FIG. 2 and is generally indicated by reference character lb. The apparatus lb comprises a charge-retentive belt or web l? which may, for example, consist of a conducting base of brass or electroformed nickel having disposed thereon a photoconductive layer of well known composition as found in the art. The belt ll'7 is transported by upper and lower roller members l8, only the lower one of which is shown.

A charging device 119 is provided, which in accordance with well known principles, places a uniform electrostatic charge on the web at it passes thereunder. Although other charging devices known to those skilled in the art may be utilized, it is preferable to charge the photosensitive web by corona discharge from a wire filament or wire filament array which is maintained at a high potential as described, for example, in US. Pat. Nos. 2,588,699 to Carlson, 2,836,726 to Vyverberg, 2,777,957 to Walkup, 2,778,946 to Mayo and others. The belt is then exposed to an object or material to be reproduced through a lens structure 211. A conventional lamp, not shown, provides necessary light activity to discharge areas of the belt in accordance with light reflected from the object to thereby leave a latent electrostatic image on the belt. The belt having the latent image is then moved through a housing structure or shell 22 having a substantially l-shaped configuration having an upwardly and outwardly extending wall 25. A two-component developer 23 which is the same as the material 113 is contained in the housing structure, the toner component thereof being attracted to the image bearing surface. The belt is moved in an upward direction intermediate a vertically oriented partition 24 and a web guide or support 26. While the circulation of the developer material is similar, in the developer supply or sump area, to that described with reference to FIG. 1, the present apparatus differs in that the developer material is carried upwardly between the web and the partition to the top edge of the partition where if falls back to the developer supply on the reverse side of the partition in an area intermediate the partition and the housing structure. With a uniform spacing of 0.12 inch between the partition and the web 17 and with a web speed of approximately 6 inches per second, a laminar flow of developer material is created through a frictional force established between the web and the developer material. The partition may be fabricated from various materials, for example, aluminum. The developer contacting side of the partition is preferably smooth to thereby minimize toner buildup thereon.

A baffle member 27 attached to the partition 24 intercepts the unused developer materials from the supply as well as toner particles 28 which are added to the developer supply from a toner hopper or dispenser 29. The dispenser 29 may be of any conventional construction suitable for metering toner at a desired rate, so long as the outlet therefrom is disposed above the baffle 27 as shown. A structure suitable for this application is described in US. Pat. No. 3,013,703 issued in the name of R. A. Hunt.

The developed image is transferred to a transfer web 31 with the image being subsequently rendered permanent by suitable fusing means, not shown. The belt is then cleaned in a conventional manner whereupon the belt is ready for another cycle of operation. A transfer corotron 32 is provided for' accomplishing transfer to the web.

It will now be apparent that there has been disclosed an improved electrostatic recording apparatus wherein an improved developer supply is attained through cross mixing of already used developer material with newly added toner. To this end the bafile structure 27 causes the aforementioned material to be mixed prior to the return to the sump area thus overcoming the problem of stagnated pockets of toner and/or already used developer materials. Furthermore, longer contact is provided between developer and recording medium thereby providing a system capable of operational speeds which are greater than those heretofore found in the prior art.

While the present invention has been described with reference to the particular structure disclosed herein, it is not intended that it be limited to the specific details and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or scope of the claims forming a part hereof. For example, the partition and baffle members 24 and 27 could be replaced by a triangular-shaped belt arrangement mounted for free movement by the upward movement of the developer material. One side of the belt would occupy the plane of the partition 24 while another side thereof would be in the plane of the baffle 27. Alternatively, the partition alone could be replaced by a freely movable .belt which would cooperate with a stationary baffle similar to the bafile 27. The effect of the foregoing, it is thought, would enhance the laminar flow of the developer material due to the reduced frictional effects.

What is claimed is:

1. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising:

movable charge-retentive surface; housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surfac by said developer material;

means for moving said charge-retentive surface through a supply of developer ink in said housing and then in an upward direction;

means disposed in said housing structure cooperating with said movable surface for effecting upward movement of developer, the spacing between said movable surface and said means disposed in said housing structure being substantially equal over the full extent of said means disposed within said housing structure;

toner dispensing means disposed above said sump area and intermediate said partition and upwardly extending wall of said housing structure whereby dispensed toner is mixed with carrier material and unused toner prior to their return to the developer sump area; and

baffle structure vertically disposed intermediate the outlet from said toner dispenser and the top level of developer in said sump, said baffle structure being so positioned as to form a mixing zone for newly added toner and unused toner and carrier particles.

2. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising:

a movable charge-retentive surface;

housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surface by said developer material;

means for moving said charge-retentive surface through a supply of developer ink in said housing and then in an upward direction;

means disposed in said housing structure cooperating with said movable surface for effecting upward movement of developer, the spacing between said movable surface and said means disposed in said housing structure being substantially equal over the full extent of said means disposed within said housing structure, said means disposed in said housing structure comprising a stationary partition.

3. Structure as specified in claim 2 wherein,

the spacing between said partition and an upwardly extending wall of said housing structure is greater at the top of said wall than at the bottom.

4. Structure as specified in claim 3 wherein,

said movable charge-retentive surface comprises an elongated recording web.

5. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising:

a movable charge-retentive surface;

housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surface by said developer material;

unused toner prior to their return to the developer sump area; and

baffle structure vertically disposed intermediate the outlet from said toner dispenser and the top level of developer in said sump, said baffle structure being so positioned as to form a mixing zone for newly added toner and unused toner and carrier particles;

said bafi'le structure being integral to said partition and inclined at an acute angle thereto such that mixed materials slide downwardly into the housing structure. 

1. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising: movable charge-retentive surface; housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surface by said developer material; means for moving said charge-retentive surface through a supply of developer ink in said housing and then in an upward direction; means disposed in said housing structure cooperating with said movable surface for effecting upward movement of developer, the spacing between said movable surface and said means disposed in said housing structure being substantially equal over the full extent of said means disposed within said housing structure; toner dispensing means disposed above said sump area and intermediate said partition and upwardly extending wall of said housing structure whereby dispensed toner is mixed with carrier material and unused toner prior to their return to the developer sump area; and baffle structure vertically disposed intermediate the outlet from said toner dispenser and the top level of developer in said sump, said baffle structure being so positioned as to form a mixing zone for newly added toner and unused toner and carrier particles.
 2. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising: a movable charge-retentive surface; housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surface by said developer material; means for moving said charge-retentive surface through a supply of developer ink in said housing and then in an upward direction; means disposed in said housing structure cooperating with said movable surface for effecting upward movement of developer, the spacing between said movable surface and said means disposed in said housing structure being substantially equal over the full extent of said means disposed within said housing structure, said means disposed in said housing structure comprising a stationary partition.
 3. Structure as specified in claim 2 wherein, the spacing between said partition and an upwardly extending wall of said housing structure is greater at the top of said wall than at the bottom.
 4. Structure as specified in claim 3 wherein, said movable charge-retentive surface comprises an eLongated recording web.
 5. Apparatus for developing a latent electrostatic image on a charge-retentive surface, said apparatus comprising: a movable charge-retentive surface; housing structure capable of holding a quantity of developer material and being so constructed as to cause contacting of said charge-retentive surface by said developer material; means for moving said charge-retentive surface through a supply of developer ink in said housing and then in an upward direction; means disposed in said housing structure cooperating with said movable surface for effecting upward movement of developer, the spacing between said movable surface and said means disposed in said housing structure being substantially equal over the full extend of said means disposed within said housing structure, toner dispensing means disposed above said sump area and intermediate said partition and upwardly extending wall of said housing structure whereby dispensed toner is mixed with carrier material and unused toner prior to their return to the developer sump area; and baffle structure vertically disposed intermediate the outlet from said toner dispenser and the top level of developer in said sump, said baffle structure being so positioned as to form a mixing zone for newly added toner and unused toner and carrier particles; said baffle structure being integral to said partition and inclined at an acute angle thereto such that mixed materials slide downwardly into the housing structure. 